Portable self-contained pressurized air device for casting



April s, 1969 PORTABLE SELF-CONTAINED PRESSURIZED AIR DEVICE FOR CASTING Filed Feb. 25, 1966 B. E. JOHNSON ET AL INVENTORS BURT E. JOHNSON BYPHILLIP B. WEBB JR.

A T TORNE YS United States Patent ILS. Cl. 164-285 1 Claim c www...

ABSTRACT F THE DESCLSURE A portable wholly hand operated casting device is provided for forcing molten metal into a cavity within a mold. The device includes a reservoir with a hand pump mounted thereon for pressurizing the reservoir. The lower end of the reservoir includes a movable valve stem adapted to be engaged by an annular plate incorporating a suitable annular gasket structure for engaging the top end of a mold. Downward pressure exerted manually on the reservoir results in movement of the valve stem to release the pressurized air directly into the top of the mold and thus force the molten metal into the mold cavity.

This invention relates generally to investment or lost Wax casting and more particularly `to a device for forcing molten metal into a mold during an investment or lost wax casting process.

The art of investment or lost wax casting is old and well known. In its basic aspects, the casting process involves investing a wax or plastic specimen within a mixture of plastic, ground silica, and waterknown in the art as the investment-contained within a casting ring or flask. The ring is then placed in an oven and heated until the wax or plastic specimen is melted and burned away leaving a mold cavity or void in the investment conforming to the shape of the specimen. Upon removal of the ring from the oven, a metal such as a gold alloy, tor example, is melted in a top portion of the ring and is then forced into the mold cavity where the metal hardens into a casting conforming to the shape of the cavity. The investment is then removed from the ring to free the casting for further finishing steps as may be required.

In the above-described process, the step of forcing the molten metal into the mold cavity must be accomplished quickly while the metal is in a molten state and, moreover, must be accomplished in such a manner that the metal completely lls the mold without porosity in the casting itself. Towards this end, various equipment has been used with varying degrees of success. However, this equipment has invariably been complex and expensive such that the costs of the process have been excessive, particularly for the hobbyist or others who used the process on a limited basis.

An example of previously used equipment for forcing the metal into the mold is a high speed centrifuge type machine which receives the mold and molten metal, which then are rotated at high speeds causing the metal to flow into the mold by centrifugal force. The disadvantages of such a system are numerous and include high costs of equipment, operation, and maintenance along with the danger of spraying the operator and equipment with hot molten metal.

Another example involves the use of a source of pressurized air and tubes, valves, and the like for conducting and controlling the flow of pressurized air to a mechanism which is designed to receive the mold and conduct the air into the mold. As with the lirst mentioned example, this system is complex and expensive and is not readily portable, which electively reduces its capabilities and uses, particularly for a hobbyist.

With the foregoing in mind, it is accordingly a primary object of this invention to provide a greatly simplied casting device for quickly and elliciently forcing molten metal into a mold during a casting process.

More particularly, it is an object to provide a unitary portable device for forcing molten metal into a mold, thereby eliminating the need for complex, expensive, and permanently installed equipment heretofore required.

Another object is to provide an improved casting device which is simple and rugged in construction to the end that costs of manufacturing and maintenance are greatly reduced from those involved with equipment heretofore used.

Briefly, these and many other objects and advantages of this invention are attained by providing a unitary casting device including a self-contained source of pressurized air and means for engaging a mold, whereby air may be directed against molten metal on the mold to force the metal into a cavity within the mold.

The casting device includes a generally tubular reservoir and a hand-operated pump mounted thereon for pressurizing the reservoir. The means for engaging the mold includes a pressure head assembly, which is coupled to a valve unit on the reservoir. The pressure head assembly and valve unit are arranged such that when the pressure head assembly is pressed into engagement with the mold, continued downward movement of the reservoir with respect to the pressure head assembly opens the valve unit to direct pressurized air from the reservoir into the mold to thus force the molten metal into the cavity within the mold.

The casting device is lightweight and compact so as to be easily handled by the operator.

A better understanding of the invention will now be had by referring to a preferred embodiment thereof as illustrated in the accompanying drawings, in which:

FIGURE 1 is a sectional View of the casting device in accordance with the invention; and

FIGURE 2 is a fragmentary sectional view of the casting device of FIGURE 1 shown in operational relationship with a mold assembly.

Referring first to FIGURE l, it will be seen that the casting device generally includes a hand pump assembly mounted on a tubular air reservoir 11. A pressure release valve assembly 12 is mounted on the reservoir 11 and a pressure head assembly 13 is, in turn, coupled to the valve assembly 12.

The details of the preferred embodiment of the casting device will now be described. The pump assembly 10 includes a pump cylinder 14 having a threaded cap 15 secured to an end thereof `as shown. Defined through the cap 15 is an opening 16 which is adapted to receive a pump rod 17. The pump rod 17 is provided with an enlarged diameter knob 18 by which the rod may be gripped to be reciprocated within the pump cylinder 14.

A cup-type piston member 19 made, for example, of leather is secured to the pump rod 17 between a pair of spaced washers 20 and 21, respectively. The piston 19 and washers 20 and 21 are secured to the pump rod 17 by means of a threaded nut 22. A coil spring 23` is mounted around the pump rod 17 and serves as a spring cushion against the end cap 15 when the pump rod is drawn upwardly on its upstroke.

Upon actuation of the hand pump assembly 10, air is transmitted into the air reservoir 11 through a conventional poppet valve assembly 24. This valve assembly includes a valve casing 25 being threadedly coupled to an air outlet nipple 26 which is, in turn, threadedly coupled to the pump cylinder 14. A valve member 27 is disposed within the Valve casing 25 and is normally biased upwardly into engagement with the nipple 26 by means of a coil spring 28. It will be apparent that upon each upstroke of the rod and piston, air will pass about the periphery of the piston to ll the resulting void in the cylinder 14. This air may enter the upper portion of the cylinder 14 about the rod opening 16. Upon each downstroke of the pump rod 17 and piston 19, the periphery of the piston will are out into sealing relationship with the cylinder walls and air will be compressed within the pump cylinder 14 and will force the valve member 27 downwardly against the spring 28 to accordingly permit the air to pass into the reservoir 11 through air passages 29 defined in the valve casing 25. Of course, upon completion of the downstroke, the spring 28, together with the air pressure within the reservoir 11, will force the valve member 27 upwardly to close the air outlet nipple 26.

The above described hand pump assembly is mounted within an end cap 30 which is threadedly coupled to the upper end of the reservoir cylinder 11. In a somewhat similar manner, the lower end of the reservoir cylinder 11 is threaded to receive a second end cap 31.

In accordance with an important feature of the invention, the casting device includes a valve assembly 12 (heretofore mentioned) through which pressurized air may be released from the reservoir 11 into a mold or casting assembly to be subsequently described. The end cap 31 is provided with a centrally disposed cylindrical flange 32 which terminates in an annular seating edge 33. The cylindrical ange 32 denes an opening 34 which is adapted to receive a valve stem 35 which terminates at its upper end in an increased diameter annular flange 36 and at its lower end in a threaded portion 37.

The valve stem 35 includes a central passage 38 communicating with a pair of diametrically opposed transverse passages 39 and 40 through which pressurized air may pass outwardly from the reservoir 11 in a manner to be subsequently described.

In order to Lmaintain pressurized air within the reservoir 11 until it is desired to release the same, a first O- ring 41 is tightly tted around the valve stern 35 adjacent to the annular ange 36 and is positioned in sealing engagement with the annular seating edge 33 of the cylindrical flange 32 when the valve assembly 12 is in a closed position shown in FIGURE 1. A second O-ring 42 is secured around the valve stem 35 below the transverse passages 39 and 40 to sealingly engage the cylindrical flange 32 and thereby prevent escape of pressurized air between the valve stem 35 and the flange 32 when the valve assembly 12 is in an open position to be described with reference to FIGURE 2.

A particularly important feature of the invention resides in the provision of a pressure head assembly 13 (heretofore mentioned) which is adapted to engage a mold ring and direct pressurized air from the reservoir 11 into the mold. Towards this end, the pressure head assem=bly 13 includes an annular plate portion 43 threadedly coupled to the threaded portion 37 of the valve stem 35. The plate portion 43 includes a cylindrical sidewall portion 44 which terminates at its bottom end in an inturned annular ange 45. An annular sealing gasket 46 made, for example, of rubber and `an annular insulating gasket 47 made, for example, of asbestos are positioned within the cylindrical sidewall portion 44 and are retained in place by the inturned annular ange 45.

In order to maintain the valve assembly 12 in the closed position illustrated in FIGURE 1, a coil spring 48 is disposed around the valve stem 35 and is interposed between the end cap 31 and the plate portion 43 of the pressure head assembly 13. The spring 48 acts to bias the valve stem 35 downwardly to thereby compress the O-ring 41 between the annular flange 36 and the seating edge 33. Accordingly, pressurized air within the reservoir 11 is prevented from escaping through the valve assembly 12. It will, of course, be apparent that air pressure within the reservoir 11 will aid in maintaining the valve stem assembly 12 in the closed position by acting downwardly against the top of the valve stem 35.

Referring now to FIGURE 2, the casting device is shown positioned on the top of a cylindrical casting ring 49 which encloses a refractory material 50 which, as above described, may comprise a hardened mixture of plastic, ground silica, and waterknown in the art as the investment. The investment 50 is formed with a conical crater 51 communicating with a downwardly extending passage 52 called a sprue, which, in turn, communicates with a mold cavity Or void 53 shaped to the desired form of the object to be cast therein.

After heating the ring 49 and the enclosed investment 50 in a heating oven, the ring is removed therefrom and placed upon a table or supporting surface 54 and a metal is melted in the crater 51 until it iiows or pools into the position shown in dotted lines at 55.

The surface tension of the molten metal 55 prevents it from flowing downwardly through the sprue 52 into the mold cavity 53, and, accordingly, the molten metal must be forced to flow quickly into the mold cavity 53 before the metal cools and hardens within the crater 51.

The foregoing is achieved by the casting device of the invention, the operation of which will now be described. First, the hand pump assembly 10 is actuated to pressurize the reservoir 11. The device is then placed over the casting ring 49 with the pressure head assembly 13 in contact with the top of the ring 49. The reservoir 11 is then pushed downwardly with respect to the pressure head assembly causing the valve assembly 12 to open as shown in FIGURE 2. The air within the reservoir then passes through the passages 39 and 40 into the passage 38 and then into the crater 51 where the air pressure forces the molten metal downwardly through the sprue 52 into the mold cavity 53.

The air pressure is sufficient to force the metal into the cavity quickly before the metal hardens and also insures that the metal completely fills the cavity without porosity in the finished casting.

The insulating gasket 47 serves to prevent transfer of heat from the ring 49 to the pressure head assembly, and the resilient sealing gasket 46 insures that the pressurized air will not escape its path from the pressure head assembly into the ring 49.

After completion of the above-described casting operation, the casting device is simply lifted off the ring 49 and the spring 48 acts to close the valve assembly 12, thereby permitting the reservoir to be again pressurized in preparation for subsequent casting operations.

The casting device is uniquely constructed to accommodate casting rings of a variety of diameters and, as is apparent, can be used with rings of any height.

From the foregoing, it is apparent that this invention provides a compact, simplified, and easily handled casting device which may be used in conjunction with a variety of casting rings.

While the invention has been described for use in investment or lost wax casting operations, it will be understood that the invention is not to be thought of as limited to that particular use or to the specific embodiment shown and described.

What is claimed is:

1. A portable unitary hand casting device for forcing molten metal into a mold during a lost wax casting operation, said device comprising:

(a) a tubular reservoir for containing pressurized air, said reservoir including rst and second end caps mounted on its opposite ends, respectively;

(b) a tubular hand pump assembly secured through said irst end cap for pressurizing said reservoir, said hand pump assembly including a pump rod extending outwardly from said first end cap for actuating said hand pump assembly to pressurize said reservoir;

(c) a pressure release valve stem mounted for in and out telescopic movement n said second end cap, said second end cap delining an internal valve seat for said valve stem so that when said valve stem is telescoped inwardly, said seat is uncovered to communicate pressure through said valve stern;

(d) a pressure head assembly including an annular plate portion secured to the outer end of said valve stem, said plate portion having:

(l) a cylindrical side wall portion terminating in a reduced diameter annular flange;

(2) an annular resilient gasket positioned within Said side wall portion;

(3) an annular insulating gasket interposed Ibetween said resilient gasket and said annular ange for engaging and hermetically sealing against the top end of said mold to prevent transfer of heat from said mold to said valve stern and said reservoir means; and

(e) spring means disposed between said annular plate portion and sai-d second end cap for normally biasing said valve stem to a closed seated position,

whereby said casting device may be held solely in the hands and said annular insulating gasket manually positioned over sai-d top end of said mold, manual movement of said reservoir means downwardly with respect to said annular plate Iportion telescoping said valve stem inwardly in opposition to said spring means to thereby pass pressurized air into said mold.

References Cited UNITED STATES PATENTS 1,320,824 11/1919 Bailey et al. 164-285 1,723,071 8/1929 Pitman 164-307 FOREIGN PATENTS 527,856 8/1921 France.

J. SPENCER OVERHOLSER, Primary Examiner. R. D. BALDWIN, Assistant Examiner.

U.S. C1. X.R. 164-120 

